The present invention relates to the intensification of images captured on photographic plates. More specifically, one embodiment of the invention relates to irradiating an emulsion which has had its silver crystals partially or completely replaced by another element which may be activated so that an autoradiograph can be obtained therefrom. In another embodiment, an autoradiograph is produced by replacing the silver crystals with a radionuclide.
There are many examples in which an image may be captured on a photographic emulsion or plate, but in which the image is so faint that it is too indistinct to be of any value. One example lies in the field of Astronomy, where faint astronomical objects are recorded on photographic plates by means of large telescopes and lengthy exposures. Another example lies in the filed of X-radiography wherein a patient is exposed to damaging X-rays for the purpose of capturing an X-ray image on a photographic emulsion. In both of these instances, it would be desirable to reduce the necessary exposure time. In the first instance, if it were possible to photograph faint sources with a reduced exposure time, the efficiency and productivity of the telescope would be substantially increased. In the second instance, a reduced exposure of the patient to the damaging X-rays would be beneficial to the patient. Thus, a method which would intensify the image of a photographic plate is extremely desirable.
Such a method is known in the prior art and is disclosed in the April, 1974 issue of the bulletin of the American Physical Society, page 600. This prior art process proposes taking an exposed photographic emulsion on which an image has been captured in a pattern of silver crystals and irradiating the silver crystals with a neutron flux, thereby activating the silver crystals to radioactive silver isotopes. From this activated plate or emulsion, an autoradiograph is obtained by placing a second photographic emulsion in contact with the first activated photographic emulsion. But this prior art process suffers from the difficulty that the image intensification is limited by the neutron cross-section of the silver nucleus. Thus, is posed the problem of finding a method which would permit greater image intensification so that already recorded, although indistinct images on astronomical plates may be examined, and so that exposure times of both the astronomical telescope or the X-ray machine may be reduced. This object is realized by the present invention through the recognition that the silver atoms of the photographic emulsion may be replaced by the atoms of a "secondary element." By "secondary element" is meant an element which has properties which are more desirable than silver for the purpose of obtaining an enhanced image. Such secondary elements may have larger neutron cross-sections than silver, may decay with the emission of radiations which are more reactive with matter than the beta rays emitted by the radioactive decay of activated silver, may be a fissionable element, or may be a radioisotope.